<div class="wrapper">
  <div class="sidebar">
    <ul>
      <li><li>
      <li><li>
      <li><li>
      <li><li>
      <li><li>
      <li><li>
      <li><li>
    </ul>
  </div>
  <div>
    <h1 class="title">Change the browser's font size</h1>
    <p>notice how the breakpoint scales with browser setting</p>
    <p class="desc">Window width: <span id="js-width"></span></p>
    <div class="rem-container">
     <h2 class="rem">One REM is this many pixels:</h2>
      <span class="box"></span>
      <span class="box-size"></span>
    </div>
  </div>
</div> 

// define root font size here, it is assumed that most browsers default to 16px as their default font size
$html-font-size: 16px;
@function stripUnit($value) {
    @return $value / ($value * 0 + 1);
}
@function rempx($pxValue) {
    @return #{stripUnit($pxValue) / stripUnit($html-font-size)}rem;
}

html, body {
  // important not to reassign 1rem to 10px 
  // the font-size must stay 100% (or just not declared at all)
  // font-size: 100%;
}

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

.wrapper {
  font-family: Arial, Helvetica, sans-serif;
  min-height: 100vh;
  background: #C5AAB7;
  display: grid;
  place-items: center;
  align-content: center;
  justify-items: center;
  transition: grid .5s, background .3s ease, color .3s;
  font-size: 1rem;
  grid-template-columns: 200px 1fr;
  column-gap: rempx(20px);


  //  *********************
    // you write a pixel value, get a scaling rem value
  @media only screen and (min-width: rempx(1000px)) {
  //  *********************
    grid-template-columns: min(#{rempx(500px)}, 30%) 1fr;
    background: #496DDB;
    color: white;
  }
}

.title {  
  font-size: 2em;
  margin-bottom: rempx(8px);
}

.title + p {
  margin-bottom: rempx(16px);
}


.desc {
  font-size: 1em;
  margin-bottom: rempx(60px); 
}

.rem {
  font-size: 1.5em;
  margin-bottom: rempx(6px);
}

.sidebar {
  height: 100vh;
  width: 100%;
  
  ul {
    display: flex;
    flex-direction: column;
    height: 100%;
    justify-content: stretch;
    align-items: stretch;
     
    li {
       height: 100%;      
       &:nth-of-type(odd) {
         background: white;
       }
    }
  }
}

.rem-container {
  display: flex;
  align-items: center;
  width: fit-content;
}

.rem {
  font-size: 1em;
}

.box {
  display: inline-block;
  width: 1rem;
  height: 1rem;
  background: black;
  color: white;
  margin-left: rempx(20px);
  font-size: 1rem;
}
.box-size {
  margin-left: rempx(8px);
  display: inline-block;
}

const width = document.querySelector('#js-width');
const box = document.querySelector('.box');
const boxSize = document.querySelector('.box-size');

const calculateWidth = () => {
  width.innerText = `${parseInt(window.innerWidth)} px`;
}

calculateWidth();
window.onresize = calculateWidth

boxSize.append(Math.round(box.getBoundingClientRect().width))